Modification by drugs of the secretagogue effect of dopamine on the pancrease.

1 The specific stimulating action of dopamine and L-DOPA on exocrine pancreatic secretion was further investigated in the isolated blood-perfused canine pancreas.2 6-Hydroxydopamine (100 mug, i.a.) stimulated the secretion but was far less potent than dopamine. Epinine (0.3-1 mg. i.a.), alpha-methyldopamine (10-300 mug, i.a.) and octopamine (10-300 mug, i.a.) were ineffective.3 alpha-Methyldopa (30 mg, i.a.) inhibited the stimulating effect of L-DOPA (1-3 mg) on pancreatic secretion.4 Apomorphine (1 mg, i.a.) attenuated dopamine-induced (1-30 mug) pancreatic secretion but did not antagonize secretin-induced (0.03-0.3 units) or pancreozymin-induced (0.3-1 units) secretion.5 These observations suggest that L-DOPA is probably converted to dopamine to stimulate the exocrine pancreas, and that dopamine interacts with the specific receptors.6 The noradrenaline and dopamine content of the canine pancreas was estimated in controls and in dogs treated with secretin, reserpine, L-DOPA or alpha-methyldopa. The values for dopamine and noradrenaline in controls were 139 +/- 6 and 375 +/- 40 ng/g tissue (n=13), respectively. Reserpine reduced the noradrenaline content of the pancreatic tissue without affecting the dopamine content. L-DOPA or secretin caused a significant increase in the dopamine, but not in the noradrenaline content. It is suggested that dopamine has a physiological function in the pancreas which is independent of that of the noradrenaline-containing nerve fibres.